Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$137.93	8.221%	$149.2692	$149.27	$149.25	$149.30
Purchase #2	$47.41	12.485%	$53.3291	$53.33	$53.35	$53.30
Purchase #3	$19.32	6.224%	$20.5225	$20.52	$20.50	$20.50
Purchase #4	$30.81	3.406%	$31.8594	$31.86	$31.85	$31.90
Purchase #5	$134.52	9.191%	$146.8837	$146.88	$146.90	$146.90
Purchase #6	$191.25	12.458%	$215.0759	$215.08	$215.10	$215.10
Purchase #7	$176.49	3.468%	$182.6107	$182.61	$182.60	$182.60
7 purchase totals =	$737.73		$799.5505	$799.55	$799.55	$799.60